Compact Quantum Dots Photoligated with Multifunctional Zwitterionic Coating for Immunofluorescence and Imaging

Integration of nanomaterials with biotechnology requires the development of optimized coating strategies that provide extended colloidal stability and compact size, while allowing controllable surface coupling of the nanocrystals to target biomolecules [1] , [2] . Here, we detail the design and optimization of a set of multicoordinating ligands that combine the benefits of mixed coordination (thiol and imidazole) with molecular-scale zwitterion motifs, yielding sterically stabilized and compact nanocrystals ( Fig. 1 ) [3] – [5] . These QDs present a controllable number of azide groups for easy conjugation to biomolecules via click chemistry. The polymer coating is characterized using several complementary analytical techniques, including NMR spectroscopy, to extract estimates of the hydrodynamic size and the surface ligand density. Conjugating the resulting QDs to antitropomyosin receptor kinase B antibody (α-TrkB), or to the brain-derived neurotrophic factor (BDNF), has allowed successful labeling of the tropomyosin receptor kinase B (TrkB) in pyramidal neurons within cortical tissue. It has also allowed visual monitoring of BDNF-induced activation of TrkB signaling in live neuronal cells ( Fig. 1 ) [4] .